This invention relates to seal segments for gas turbine engines. More particularly, but not exclusively, the invention relates to seal segments for high pressure turbines of gas turbine engines. The invention also relates to wall structures for turbines formed of a plurality of seal segments.
In gas turbine engines seal segments form a seal segment ring around the turbine blades of the engine. These seal segments can overheat because of leakage of hot gases flowing through the turbine around the tips of the turbine blades. This is a particular problem in high pressure turbines.
According to one aspect of this invention there is provided a seal segment for a seal segment ring of a gas turbine engine, the seal segment comprising a main body having an inner surface adapted to face the turbine blades in use, wherein path means for a cooling fluid is defined in the main body, the path means extending, in use, between upstream and downstream regions of the seal segment.
The main body may be formed as a one piece element.
According to another aspect of this invention there is provided a seal segment for a seal segment ring of a gas turbine engine, the seal segment having an inner surface adapted to face the turbine blades in use, wherein path means is defined in the seal segment, the path means being adapted to extend, in use, between upstream and downstream regions of the seal segment, and having downstream inlet means through which a cooling fluid to cool the segment can enter the path means and upstream outlet means from which the cooling fluid can be exhausted from the path means, whereby cooling fluid can flow along the path means in a generally upstream direction opposite to the flow of gas through the turbine.
The outlet means is preferably arranged, in use, upstream of the turbine blades. In one embodiment, the outlet means for the cooling fluid is arranged to open in a downstream direction. In another embodiment, the outlet means is directed generally radially inwardly. Thus, in these embodiments, cooling fluid exhausted from the path means may pass over said inner surface of the segment in a downstream direction. The outlet means may be directed, in use, at an angle to the principal axis of the turbine, such that cooling fluid exits from the path means in substantially the identical direction to the flow of gas through the turbine at said outlet means.
The path means preferably extends, in use, generally parallel to the principal axis of the turbine. A preferred embodiment of this invention has the advantage that improved heat transfer is achieved by the provision of path means in which the flow of cooling fluid is from a downstream region of the seal segment to an upstream region. The flow of the cooling fluid in the path means in this preferred embodiment is counter to the main flow of gas through the engine, having the advantage of increasing heat transfer. The inlet means may be angled, in use, relative to the principal axis of the turbine such that the flow of the cooling fluid through the path means is substantially directly opposite to the flow of gas through the engine.
The path means preferably extends to one or more regions of the main body adjacent the inner surface to provide cooling at the, or each, of said regions in use.
Preferably, the path means comprises at least one passage which is preferably elongate, and the passage may extend laterally across the seal segment, preferably in a generally circumferential direction, in use. Preferably each seal segment defines two or more of said passages, which may be defined side-by-side, and each may extend laterally across the segment part way, preferably substantially half way. The path means may comprise a plurality of such passages each passage preferably extending generally parallel to the principal axis of the turbine in use. Preferably, the path means is configured to conform substantially to the profile of said inner surface.
The seal segment may include a plurality of heat removal members in the path means. The heat removal members may be in the form of pedestals, which may extend from a radially inner wall of the path means to a radially outer wall of the path means.
The path means may comprise one or more steps. In one embodiment, the path means comprises first and second axial sections, the first section extending from the inlet means to a region upstream thereof, and the second section extending from said region to the outlet means. The first and second sections may axially overlap and a conduit may extend between the first and second sections in said region. The configuration of said conduit is preferably arranged to produce impingement cooling of said seal segment by the cooling fluid as it enters the second section from said conduit. Alternatively, or in addition, the configuration of the conduit may be arranged to produce cooling of the seal segment by other enhanced heat transfer mechanisms. In another embodiment the path means comprises a single axial section which may include one or more steps.
In one embodiment, the path means extends to one or more regions of the seal segment adjacent the inner surface of the seal segment.
According to another aspect of this invention, there is provided a seal segment ring for a turbine of a gas turbine engine, the seal segment ring being formed from a plurality of seal segments as described above, the segments being arranged, in use, circumferentially around the turbine.
Preferably, the path means of successive segments defines a plurality of axially extending passages arranged side-by-side circumferentially around the seal ring to define an annulus of said cooling passages.
According to another aspect of this invention there is provided a core for use in a method of making a seal segment, the core comprising a main portion to form path means in the seal segment and projection means extending therefrom. In the preferred embodiment, the projection means is so arranged on the main portion and so configured to minimise the amount of material used in the method.
Preferably, the projection means is arranged generally centrally of the core conveniently on a substantially central axis. The projection means may comprise a first projection extending from a first surface of the main portion, and a second projection extending from a second surface of the main portion. The first surface is preferably a longitudinally and laterally extending surface. The second surface is preferably an edge surface, conveniently a laterally extending edge surface.
The first projection may have a generally cylindrical region, and the second projection may have a generally conical main region. The first projection may include a connecting region to connect the main region to the surface, the connecting region tapering outwardly from the main region.